qa/cephfs: check before mounting fuse connections directory

qa/cephfs: check before mounting fuse connections directory

Check if "/sys/fs/fuse/connections" is already mounted before attempting
to mount it again. Doing so leads to unnecessary error messages in the
vstart_runner.py's output (and most likely in logs for teuthology test
runs too) which confuses the users. See end for the error message.

Also, remove "check_status=False" so that the when the commands crashes
the testing is halted immediately. Initially, this must've been added to
ignore errors generated from re-mounting FUSE connections directory
repeatedly.

The error message -

DEBUG:__main__:> sudo mount -t fusectl /sys/fs/fuse/connections /sys/fs/fuse/connections
mount: /sys/fs/fuse/connections: /sys/fs/fuse/connections already mounted or mount point busy.

Signed-off-by: Rishabh Dave <ridave@redhat.com>